UNIVERSITY    OF   CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,  CALIFORNIA 


THE  UTILIZATION  OF  SURPLUS 

PLUMS 


W.  V.  CRUESS 


BULLETIN  400 

February,  1926 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1926 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/utilizationofsur400crue 


THE  UTILIZATION  OF  SURPLUS  PLUMS 

W.  V.  CRUESS 


Most  of  the  plums  grown  in  California  are  marketed  in  the  fresh 
condition,  but  owing  to  the  fact  that  special  qualities  are  necessary 
for  this  purpose,  much  fruit  is  left  on  the  trees,  or  is  sorted  out  as 
culls  at  the  packing  houses. 

Estimates  by  Farm  Advisor  McCallum  and  others  place  the  aver- 
age amount  of  cull  plums  in  Placer  County  at  about  3000  tons.  Placer 
County  had  in  1924  approximately  7,350  acres  of  bearing  plums,  ac- 
cording to  statistics  of  the  State  Department  of  Agriculture,  and  the 
remainder  of  the  State  approximately  21,400  acres.  Assuming  that 
the  amount  of  culls  to  the  acre  is  the  same  for  other  plum  districts 
as  for  Placer  County,  the  total  quantity  of  cull  plums  would  be  about 
12,000  tons  annually. 

At  present  only  a  very  small  proportion  of  the  cull  plums  is 
utilized ;  jam  factories  in  California  being  the  principal  users.  Some 
plums  are  used  locally  in  the  home  for  jams  and  jellies,  but  the  total 
so  used  is  insignificant.  If  a  market  for  the  low  grade  fruit  for  use 
in  by-products  could  be  developed,  it  would  result  in  great  benefit 
to  the  industry,  both  directly  by  increasing  returns  and  indirectly  by 
preventing  the  marketing  of  inferior  fruit. 

In  October,  1922,  the  University  was  requested  by  a  committee  of 
the  Farm  Bureau  of  Placer  County  to  study  methods  of  utilizing  sur- 
plus plums.  In  answer  to  this  request  experiments  were  made  at 
Berkeley  and  at  Lincoln  during  the  1923,  1924  and  1925  seasons. 

Acknowledgments. — All  of  the  experiments  under  factory  condi- 
tions were  made  in  the  cannery  of  the  Placer  County  Fruit  Growers ' 
Canning  Association  at  Lincoln,  of  which  E.  J.  Fereva  is  general 
manager,  and  H.  C.  Gordon,  superintendent. 

A.  Fereva,  foreman  of  cutting  room  and  T.  Richards,  foreman  of 
the  cook-room  actively  cooperated  in  the  experiments.  Thanks  are 
due  A.  W.  Christie  of  the  Fruit  Products  Laboratory  for  data  on  the 
dehydration  of  cull  plums,  and  J.  H.  Irish  for  observations  made  in 
1923  on  the  canned  and  bottled  samples  of  plum  products  stored  at 
Berkeley.  Acknowledgement  is  made  to  R.  D.  McCallum,  Farm 
Advisor  of  Placer  County  for  his  cooperation  throughout  the  experi- 
ments and  to  the  Placer  County  Fruit  Growers'  Association  of  Lin- 
coln, J.  A.  Teagarden  and  others  for  fruit  used. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Freezing  Storage. — Fruit  preserving  factories  use,  in  the  prepara- 
tion of  jams  and  jellies,  large  quantities  of  berries  preserved  by 
freezing.  The  barreled  berries  are  distributed  in  the  frozen  condition 
throughout  the  United  States  from  cold  storage  warehouses  located 
in  berry  districts. 

Since  plums  are  very  satisfactory  for  use  in  jams,  jellies  and 
butters,  and,  like  berries,  are  very  perishable  in  the  fresh  state,  it 
was  thought  that  they  might  be  stored  and  distributed  successfully 
in  the  frozen  condition. 

Approximately  equal  quantities  of  cull  President,  Giant  and  Grand 
Duke  plums  were  mixed.  The  fruit  used  was  in  sound  condition,  but 
varied  in  maturity  from  hard  green  to  soft  ripe. 

Experiments  with  other  fruits  had  proved  that  fruit  preserved  by 
freezing  must  be  covered  with  liquid  in  order  to  minimize  darkening 
of  the  color.  Water  could  be  added  to  the  whole  fruit,  but  would 
greatly  dilute  the  product.  The  natural  juice  of  the  crushed  plums, 
however,  has  no  such  objection.  The  best  method  of  crushing  found 
consisted  in  passing  the  plums  through  an  apple  crusher  with  the 
crushing  rolls  so  adjusted  that  the  flesh  of  the  plums  was  crushed 
without  breaking  the  pits. 

Crushing  liberated  enough  juice  to  completely  fill  the  spaces  be- 
tween the  pieces  of  fruit  and  gave  a  "solid"  pack. 

Number  ten  cans  and  a  five  gallon  and  a  ten  gallon  keg  were  used. 
The  kegs  were  filled  after  removing  one  head.  After  filling,  this  was 
replaced  and  the  hoops  driven  into  place.  The  cans  were  filled  and 
sealed  without  exhausting  or  heating. 

The  sealed  containers  were  placed  in  the  freezing  room  of  the 
Pomology  experimental  cold  storage  plant  at  Berkeley.  Resistance 
thermometers  were  placed  in  the  center  of  one  container  of  each  size 
and  readings  made  at  intervals  on  a  potentiometer  placed  outside  the 
cold  storage  room.*  The  purpose  of  the  test  was  to  determine  whether 
the  rate  of  cooling  would  be  rapid  enough  to  prevent  fermentation 
when  fruit  packed  without  previous  precooling  is  used.  In  figure  1 
will  be  found  the  cooling  curves.  Cooling  was  rapid  until  the  freezing 
point,  about  28.5°  F.,  was  reached.  The  temperature  in  the  kegs 
remained  at  this  point  for  several  hours,  probably,  as  suggested  by 
F.  T.  Bioletti,  because  the  latent  heat  of  fusion  absorbed  during 
freezing  temporarily  arrested  the  drop  in  temperature. 

The  cooling  was  sufficiently  rapid  under  the  aforementioned  condi- 
tions to  prevent  fermentation  of  sound  fruit.     A  50  gallon  barrel 


*  The  temperature  measurements  were  made  by  George  Marsh. 


Bull.  400] 


THE   UTILIZATION    OP    SURPLUS    PLUMS 


packed  with  another  variety  of  fruit  was  also  found  to  cool  sufficiently 
rapidly  to  preclude  spoiling. 

On  removal  from  cold  storage,  the  frozen  fruit  thaws  very  slowly ; 
a  50  gallon  barrel  of  other  fruit  contained  some  ice  one  week  after 
removal  from  the  cold  room.  The  barreled  fruit  could,  therefore, 
be  shipped  considerable  distances  by  ordinary  freight  without 
refrigeration. 

After  several  months'  storage  the  frozen  fruit  was  found  to  be 
equal  in  value  to  the  fresh  for  use  in  jam,  buter,  and  jelly. 


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Fig.  1. — Curves  showing  the  cooling  of  crushed  plums  in  three  sizes  of  containers 

stored  at  about  0°  F. 

Storage  at  32  F. — During  two  successive  seasons,  cull  plums  were 
taken  direct  from  the  fresh  fruit  packing  house  in  Lincoln  and  stored 
in  50  pound  lug  boxes  at  32°  F.  in  the  Lincoln  Cannery's  cold  storage 
room.  Some  loss  from  the  molding  of  overripe  fruit  occurred  and 
sorting  and  washing  at  the  time  of  removal  from  storage  was  neces- 
sary. The  cold-stored  fruit  after  about  five  weeks'  storage  was  found 
thoroughly  satisfactory  for  the  preparation  of  all  of  the  products 
described  in  this  publication. 

Storage  at  32°  F.  could  be  used  as  a  means  of  accumulating  suffi- 
cient cull  fruit  to  warrant  operation  of  a  by-products  factory  in 
localities  where  only  a  relatively  small  amount  of  any  one  variety  of 
plums  is  available  at  one  time,  but  where  the  agregate  of  all  varieties 
is  relatively  large. 

Plum  Jam  and  Butter. — It  was  found  by  extensive  trials  with 
culls  of  the  more  important  varieties  of  plums  grown  in  Placer  County 
that  excellent  plum  butter  and  jam  could  be  made.     In  small  scale 


6 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


experiments  the  single  varieties  were  used  for  each  test ;  in  factory 
scale  experiments,  several  varieties  were  mixed.  In  factory  practice, 
it  would  be  necessary  to  mix  the  different  varieties  in  order  to  obtain 
a  finished  product  of  uniform  character. 

The  cull  plums  were  first  carefully  sorted  to  remove  rot.  The}^ 
were  then  transferred  to  a  large  steam  jacketed  copper  kettle  and 
washed  thoroughly  with  cold  water.  Water  at  the  rate  of  about  6 
gallons  to  300  pounds  of  the  fruit  was  added;  this  was  enough  to 
prevent  scorching  during  cooking.  The  fruit  was  boiled  until  well 
softened,  that  is  about  15  minutes. 


Fig.  2. — Pulper.  Used  for  separating  skins  and  seeds  from  pulp  and  juice. 
(Courtesy  Anderson-Barngrover  Company).  A  similar  pulper  is  also  made  by 
the  Smith  Manufacturing  Company. 

It  was  then  passed  through  a  large  Anderson-Barngrover  tomato 
pulper  operated  at  about  300  R.  P.  M.    See  figure  2. 

In  the  pulper  the  juice  and  pulp  were  separated  from  the  seeds 
and  skins  by  means  of  a  heavy  copper  screen  against  which  the  fruit 
was  thrown  and  rubbed  by  revolving  paddles.  It  was  necessary  to 
set  the  paddles  of  the  pulper  at  a  sufficient  distance  from  the  screen 
to  prevent  rupture  of  the  screen  by  the  pits.  If  the  pulper  were  to 
be  used  continuously  on  plums,  it  would  be  advisable  to  install  a  very 
heavy  screen  because  the  abrasive  action  of  the  plum  pits  on  the 
average  tomato  screen  is  severe.     The  openings  in  the  screen  should 


Bull.  400]  THE  UTILIZATION   OF  SURPLUS  PLUMS  7 

be  larger  than  for  tomatoes  in  order  that  pieces  of  plum  flesh  would 
be  evident  in  the  pulp — a  fine  grained  pulp  is  not  so  attractive  in 
appearance  and  texture  as  a  coarse  one. 

In  preparing  plums  and  apricots  for  jam  making,  one  factory 
uses  a  Sprague-Lowe  tomato  finisher  of  the  vertical  type,  equipped 
with  a  heavy  screen  perforated  with  large  (about  *4  inch)  oblong 
openings;  the  greater  diameter  of  the  openings  being  at  right  angles 
to  the  vertical  axis  of  the  finisher.  In  this  machine  coarse,  heavy 
brushes  rub  the  flesh  through  the  screen.  A  coarse  pulp  is  obtained 
and  seeds  are  well  cleaned  of  adhering  flesh. 

In  English  jam  factories,  a  machine  similar  in  general  appearance 
to  the  Kern  tomato  finisher  is  used  in  preparing  plum  pulp  for  jam 
making.  It  consists  of  a  perforated  horizontal  metal  cylinder  in 
which  coarse  brushes  revolve  rapidly  and  rub  the  pulp  through  the 
screen.  Judging  from  results,  the  brush  form  of  pulper  (or  "finisher") 
equipped  with  a  screen  with  about  one-eighth  inch  openings  is  to  be 
preferred  to  the  tomato  pulper  for  separation  of  plum  flesh  from  the 
pits  and  skins.  Tomato  finishers  and  pulpers  are  standard  cannery 
equipment  obtainable  from  any  cannery  machinery  company.  The 
special  screens  would  probably  have  to  be  made  to  order. 

The  yields  of  pulp  varied  considerably  according  to  the  texture 
of  the  plums,  relative  size  of  pits  and  length  of  cooking.  The  average 
yield  was  approximately  159  gallons  or  about  1430  pounds  of  pulp 
per  ton  of  fruit. 

Jam  was  made  by  boiling  the  pulp  with  sugar  (and  in  some  cases 
spices)  to  the  desired  consistency  in  a  steam  jacketed  copper  kettle. 
See  figure  3.  The  usual  procedure  was  to  boil  the  mixture  until  a 
boiling  point  of  220-221°  F.,  as  indicated  by  a  jelly  thermometer, 
was  reached. 

Unspiced  jam  was  prepared  in  some  cases  with  equal  weights  of 
sugar  and  pulp ;  in  others  two-thirds  as  much  sugar  as  pulp  by 
weight.  The  use  of  the  smaller  proportion  of  sugar  yielded  a  jellied 
product  when  the  mixture  was  cooked  to  220-221°  F. — whereas  the 
jam  made  with  the  larger  proportion  of  sugar  usually  remained  semi- 
fluid. 

When  spices  were  used,  they  were  added  after  a  boiling  point  of 
219  to  220°  F.  was  reached.  They  were  first  mixed  outside  the  kettle 
with  about  1  gallon  of  the  hot  jam  in  order  to  prevent  "lumping"  of 
the  spices.  After  addition  of  the  spices,  the  jam  was  cooked  about 
two  minutes,  but  not  above  221°  F. 

The  following  amounts  of  spices  were  used  to  each  lot  of  150 
pounds  of  pulp  and  150  pounds  of  sugar ;  one  ounce  each  of  cinnamon, 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

allspice,  cloves  and  ginger.  Individual  tastes  vary  and,  on  this  account 
the  flavor  of  the  jam  made  according  to  the  foregoing  formula  would 
not  suit  all  consumers.  Plum  butter  was  made  in  exactly  the  same 
manner  as  the  jam  except  that  the  boiling  was  continued  until  a 
product  of  very  thick  consistency  was  obtained — this  was  reached 
at  223-224°  F. 

The  jam  and  butter  were  canned  scalding  hot  in  number  2% 
plain  tin  cans,  exhausted  6  minutes  at  205-210°  F.  and  sealed.  No 
further  treatment  was  given.  Sterilization  of  the  sealed  product 
was  found  unnecessary. 

The  yield  of  jam  from  150  pounds  of  pulp  and  100  pounds  of 
sugar  was  70  number  2i/>  cans.  From  150  pounds  of  pulp  and  150 
pounds  of  sugar  the  yield  varied  from  96-110  number  2%  cans, 
according  to  the  final  boiling  point  of  the  product. 

Peach-Plum  Jam  and  Butter. — In  the  Placer  County  plum  district 
there  is  available  a  considerable  quantity  of  cull  peaches.  It  was 
found  that  the  addition  of  peach  pulp  to  the  plum  gave  a  jam  of 
richer  flavor  than  that  obtained  from  plum  only. 

Hand  pitted,  lye  peeled,  pie  grade,  Tuscan  cling  peaches  were 
cooked  with  a  small  amount  of  water  (same  ratio  of  water  and  fruit 
as  for  plums,  i.e.,  1:5  by  weight)  until  soft;  pulped  in  a  tomato 
pulper  and  equal  volume  of  the  peach  and  plum  pulps  were  mixed. 
An  equal  weight  of  sugar  was  added  and  the  mixture  concentrated 
to  a  boiling  point  of  220°  F.  At  this  point,  to  150  pounds  of  pulp,  was 
added  1  ounce  each  of  cloves,  allspice,  cinnamon  and  ginger  as 
previously  described  for  plum  jam,  and  the  mixture  heated  to  221°  F. 
or  to  223-224°  F.,  according  to  whether  a  jam  of  medium  consistency 
or  a  butter  was  desired. 

The  average  yield  of  jam  was  about  100  number  2%  cans  from 
150  pounds  of  pulp  and  150  pounds  of  sugar.  In  large  scale  tests 
cull  Elberta  and  Crawford  peaches  gave  fairly  satisfactory  results 
when  used  with  plums  in  this  manner.  In  smaller  scale  laboratory 
tests,  the  Muir  and  Lovell  were  also  found  satisfactory,  in  fact, 
seemed  superior  to  the  Elberta.  Shipping  peaches  are  picked  very 
green,  consequently,  lack  flavor  when  box  ripened.  For  this  reason, 
canning  peaches  of  pie  grade  were  found  more  satisfactory  than  the 
cull  shipping  peaches. 

Canned  Pulp  for  Jam. — Plum  pulp  was  prepared  on  a  small  com- 
mercial scale  by  the  method  described  for  jam  making.  This  consisted 
in  passing  the  cooked  plums  through  a  tomato  pulper  to  separate  the 
pulp  from  the  pits  and  skins.     See  figure  2. 


Bull.  400J 


THE  UTILIZATION   OF   SURPLUS   PLUMS 


The  pulp  was  heated  to  boiling,  canned  hot,  exhausted  6  minutes 
at  200-210°  F.  to  expel  air  bubbles,  sealed,  processed  13  minutes  at 
212°  F.  in  an  agitating-  continuous  sterilizer  and  cooled  about  2 
minutes  in  running  water. 

In  a  typical  experiment,  275  pounds  of  mixed  varieties  of  plums 
was  used  and  20.5  gallons  (184.5  pounds)  of  pulp  was  obtained.  To 
fill  25  number  2%  cans,  47  pounds  of  the  pulp  was  required.  This 
corresponds  to   a   yield   of   approximately   761   number   2%    or   228 


Fig.  3. — Steam  jacketed  kettle  used  for  heating  plums  and  pulp. 


number  10  cans  per  ton  of  fresh  fruit.  The  pulp  contained  15.5  per 
cent  total  solids  determined  by  drying  10  grams  in  vacuo  at  70°  C.  for 
12  hours  and  1.74  per  cent  total  acid  (as  citric)  determined  by  titra- 
tion of  a  10  gram  sample  with  N-10  sodium  hydroxide.  Pulp  from 
the  same  fruit  to  which  no  water  was  added  contained  19.5  per  cent 
total  solids. 

The  rate  of  heat  penetration  in  number  2x/2  cans  of  plum  jam 
pulp  and  plum  butter  were  determined  by  placing  the  cans  in  a  pot 
of  water  maintained  at  the  boiling  point  and  by  reading  the  tempera- 
tures at  the  centers  of  the  cans  at  regular  intervals  by  means  of  long 
stem  chemical  thermometers.  These  were  inserted  through  rubber 
stoppers  fitted  to  openings  in  the  tops  of  the  cans.  The  following 
table  gives  the  results  of  this  test. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Rates  of  Heat  Penetration  in  Number  2j/£  Cans  of  Plum  Pulp  and 

Plum  Butter 


Temperature  at 

center  of  No.  23^ 

can  of  water 

Temperature  at  center  of  can 

Time  in  minutes 

Plum  pulp 

Plum  butter 

0 

63°  F. 
199 
205 
212 
212 
212 
212 
212 
212 
212 
212 
212 
212 

63°  F. 

99 
122 
144 
159 
172 
181 
187 
192 
196 
200 

63°  F. 

5 

8 

30 

80 

40 

94 

50 ..." 

112 

60 

129 

70 

140 

80 

149 

90 

177 

100 

110 

181 
184 

120 

188 

To  reach  a  pasteurizing  temperature  of  165°  F.  about  65  minutes 
heating  was  required  for  the  jam  pulp  and  about  85  minutes  for  the 
plum  butter.  Both  products  heated  very  slowly  because  of  their 
thick  consistency.  Water  in  a  number  2^  can  reached  the  pasteur- 
izing point  in  less  than  five  minutes. 

In  commercial  practice,  the  jam  pulp  and  butter  would  be  canned 
and  sealed  hot — probably  above  180°  F.  and  little  or  no  additional 
heating  would  be  necessary.  If,  however,  for  any  reason,  such  as  a 
temporary  shut-down  of  the  cannery,  the  products  were  canned  cold 
or  allowed  to  cool  before  sealing,  it  would  be  necessary  to  heat  them 
at  212°  F.  for  the  times  indicated  by  this  experiment  in  order  to 
bring  them  to  165°  F.  or  above. 

The  canned  pulp  was  shipped  to  Berkeley  and  either  used  in 
making  jam  and  butter  in  the  Fruit  Products  Laboratory,  or  sold  to 
Berkeley  housewives  for  jam  making.  On  the  addition  of  an  equal 
weight  of  sugar  and  boiling  to  220-222°  F.,  an  excellent  jam  (or 
butter)  of  jelly-like  consistency  was  obtained.  Several  dozen  samples 
have  been  stored  from  July,  1923  to  November,  1925 — over  two 
years — without  loss  from  corrosion  or  perforation  of  the  cans.  At 
the  present  writing,  November,  1925,  the  two  year  old  pulp  is  still 
excellent  for  making  jam  and  butter.  However,  since  the  pulp  is 
very  high  in  acid  some  loss  from  corrosion  of  the  cans  could  be 
expected  under  commercial  conditions  after  12-15  months'  storage. 


Bull.  400]  THE  utilization  of  surplus  plums  11 

Local  jam  manufacturers  state  that  the  pulp  is  suitable  for  making 
jam  commercially  and  that  there  should  be  a  market  for  a  considerable 
quantity  of  it  outside  of  California.  It  was  suggested,  however,  that 
a  very  course  screen  be  used  in  separating  the  flesh  from  the  pits 
and  that  large  cans,  number  10,  or  5  gallon  size,  be  used. 

Berkeley  housewives  in  most  instances  preferred  to  purchase  the 
jam  and  butter  instead  of  making  jam  in  the  home  from  the  canned 
pulp.  Nevertheless,  a  steady  demand  for  it  was  established  by  a  few 
demonstration  sales  on  the  campus — an  indication  that  the  product 
might  be  received  favorably,  even  for  home  use.  By  the  introduction 
of  pectin  syrup  for  home  use,  housewives  have  become  accustomed  to 
the  use  of  jelly  bases;  and  on  this  account  should  be  receptive  to  a 
jam  base  in  convenient  form. 

A  record  was  kept  of  the  fruit,  labor  and  cans  used  in  one  semi- 
commercial  experiment.  The  following  estimates  of  cost  are  based 
on  these  data: 

Estimated  cost  of  canned  pulp  from  one  ton  of  plums : 

1.  Fruit,  1  ton $15.00 

2.  Cans,  761  No.  2y2  at  3.5c 26.63 

3.  Labor,  1  man  iy2  days  at  $4.00 6.00 

4.  Cases,  labels,  steam,  etc.,  estimated  at  2c  a  can 15.22 

Total $62.85 

Estimated  cost  of  a  No.  2%  can  of  pulp S^c 

Estimated  cost  of  a  No.  10  can  of  pulp 27y2c 

One  number  2y2  can  of  pulp  gives,  with  2  pounds  of  sugar,  approxi- 
mately seven  6  ounce  jelly  glasses  of  jam.  At  a  retail  price  for  the  pulp 
of  15c  per  can  and  7c  a  pound  for  sugar,  the  cost  of  a  glass  of  jam, 
exclusive  of  fuel  and  the  jelly  glass  is  approximately  5.6c.  As  this 
is  considerably  less  than  the  retail  cost  of  ready  to  serve  jam,  the  use 
of  the  jam  pulp  would  be  economical.  Since  it  is  much  more  con- 
venient than  the  fresh  fruit  for  jam  making,  it  should  appeal  on  this 
score  also. 

Canned  Peach-Plum  Pulp  for  Jam. — Approximately  equal  volumes 
of  plum  and  peach  pulps  prepared  as  previously  described  were 
mixed,  heated  to  boiling,  canned  and  sterilized  as  described  for  plum 
pulp.  Many  of  those  who  used  both  types  preferred  the  mixed  pulp 
to  the  plum  pulp  and  for  household  use  it  might  prove  the  more 
popular.  Commercial  jam  makers,  it  was  found,  prefer  not  to  have 
the  two  varieties  of  pulp  mixed. 

Using  131  pounds  of  pie  grade  Tuscan  peaches  and  151  pounds 
of  a  mixture  of  several  varieties  of  cull  plums,  there  was  obtained  93 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

number  2%  cans  of  the  pulp  mixed  in  the  ratio  of  108  pounds  of  plum 
to  87  pounds  of  peach.  The  estimated  cost  of  a  2%  can  of  pulp  was 
approximately  8%c  and  of  a  number  10  can  approximately  29c. 
Peaches  yielded  less  pulp  than  plums,  because  of  loss  in  peeling. 
Cull  Elberta  peaches  were  used  in  one  test,  but  because  of  great 
variation  in  maturity  they  were  difficult  to  peel  uniformly  with  lye. 
The  Elberta  blended  with  the  plum  pulp  gave  a  very  satisfactory  jam 
base.  Probably  cull  peaches  of  any  standard  variety  could  be  substi- 
tuted for  Tuscan  in  this  formula. 

Jelly. — Excellent  jelly  was  prepared  on  a  small  scale  from  each 
of  the  following  varieties:  Wickson,  Santa  Rosa,  Kelsey,  Blue  Cali- 
fornia, Blue  Diamond,  Grand  Duke,  Burbank,  President,  Climax  and 
Gaviota, 

In  a  semi-commercial  test  during  the  1923  season,  jelly  was  made 
from  a  mixture  of  approximately  equal  proportions  of  Blue  Diamond 
and  Burbank  plums.  To  137  pounds  of  the  mixed  fruit  in  a  jelly 
kettle  9  gallons  of  water  were  added  and  the  mixture  boiled  until  the 
plums  were  soft — about  15  minutes.  The  juice  was  separated  from 
the  pulp  and  pits  by  straining  through  sugar  bags  and  was  made 
reasonably  clear  by  Alteration  through  a  felt  jelly  bag.  The  yield 
was  at  the  rate  of  about  200  gallons  per  ton.  The  juice  on  cooling 
to  room  temperature  was  found  to  contain  1.4  per  cent  acid  (as 
citric)  and  to  be  of  8°  Balling.  Ten  gallons  of  this  juice  concentrated 
with  52  pounds  of  sugar  to  221°  F.  gave  approximately  7%  gallons 
of  jelly.  The  jelly  was  pleasing  in  flavor,  clear,  red  and  of  firm 
texture. 

The  results  of  these  and  other  experiments  demonstrated  con- 
clusively that  packing  house  culls  of  all  of  the  commonly  grown 
varieties  of  plums  of  medium  or  high  acidity  can  be  used  for  jelly 
making.  A  red  jelly  is  preferred  and,  in  order  to  obtain  this  quality 
and  still  make  use  of  varieties  lacking  in  color,  it  is  necessary  to  add 
varieties  possessing  an  abundance  of  color.  Such  varieties  are  Blue 
Diamond,  Satsuma,  Santa  Rosa,  Grand  Duke  and  California  Blue. 
The  Blue  Diamond,  because  of  its  high  acidity,  is  particularly  desir- 
able for  jelly  making. 

Jelly  Juice. — Housewives  have  learned  to  use  various  pectin  solu- 
tions and  powders  for  jelly  making.  Jelly  manufacturers  often  store 
the  unsweetened  juices  from  boiled  fruits  and  convert  them  into 
jelly  as  the  market  demands.  The  preparation  from  plums  of  a 
jelly  juice  and  its  preservation  in  bottled  form  for  use  in  jelly  making 
is,  therefore,  not  a  new  process.  The  general  idea  being  well  known, 
it  should  not  be  difficult  to  introduce  a  meritorious  plum  jelly  juice. 


Bull.  400  J 


THE   UTILIZATION    OF   SURPLUS    PLUMS 


13 


During  both  the  1924  and  1925  seasons,  several  semi-commercial 
lots  of  plum  jelly  juice  were  prepared.  In  one  experiment,  25  gallons 
of  water  was  added  to  138  pounds  of  cull  Blue  Diamond  plums  in  a 
large  jelly  kettle.  The  water  covered  the  plums  to  a  depth  of  about 
six  inches.  The  mixture  was  boiled  20  minutes  and  the  juice  was 
recovered  by  straining  through  double  sugar  bags.  The  resulting 
juice  was  of  7°  Balling  and  contained  1.1  per  cent  acid  (as  citric). 
In  small  tests  it  gave  a  stiff  jelly  when  boiled  to  221°  F.  with  an 


Fig. 


4. — Fruit  juice  press  suitable  for  recovering  jelly  juice  from  cooked  plums. 
(Courtesy  Hydraulic  Press  Manufacturing  Company). 


equal  volume  of  sugar  and  a  soft  jelly  when  boiled  3  minutes  with 
iy2  volumes  of  sugar.  When  concentrated  to  10°  Balling  and  1.7 
per  cent  acidity,  a  firm  jelly  was  obtained  by  boiling  the  juice  4 
minutes  with  V/2  volumes  of  sugar. 

From  260  pounds  of  Blue  Diamond  culls  there  was  obtained  23 
gallons  of  jelly  juice  of  10°  Balling  and  1.7  per  cent  acidity.  This 
yield  is  at  the  rate  of  192  gallons  per  ton.  The  juice  was  bottled  in 
12  ounce  bottles  and  pasteurized  at  180°  F.  for  30  minutes.  It  was 
placed  on  sale  in  Berkeley  successfully. 

From  a  mixture  of  several  varieties  of  culls  (Santa  Rosa,  Gaviota 
and  Blue  Diamond)  a  jelly  juice  was  prepared  essentially  as  described 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

above,  except  that  it  was  concentrated  to  20°  Balling  (corrected  for 
temperature)  before  bottling.  The  yield  was  80  gallons  per  ton. 
This  juice  was  very  rich  in  pectin  and  gave  a  good  jelly  when  boiled 
3-4  minutes  with  2  volumes  of  sugar. 

A  third  lot  was  prepared  from  mixed  varieties  as  described  for  the 
Blue  Diamond  juice,  except  that  it  was  concentrated  to  only  8° 
Balling.  It  gave  an  excellent  jelly  when  boiled  "to  the  jelling  point" 
(220c  F.)  with  an  equal  volume  of  sugar. 

From  the  results  of  these  and  other  experiments  it  is  concluded 
that  the  best  method  of  preparing  jelly  juice  from  cull  plums  is  as 
follows :  Use  a  mixture  of  varieties  of  which  at  least  50  per  cent  by 
weight  consists  of  blue  or  black  or  red  varieties.  To  each  150  pounds, 
add  about  25  gallons  of  water.  Boil  until  soft.  Press  the  fruit  and 
strain  the  resulting  juice.  A  rack  and  cloth  press  is  satisfactory  for 
pressing.  See  figure  4.  Concentrate  the  juice  until  it  will  test  10° 
Balling  (corrected  for  temperature)  ;  10°  Balling  at  room  temperature 
corresponds  to  about  2°  Balling  if  the  test  is  made  at  or  near  the 
boiling  point.  Filter  the  juice.  Bottle  in  crown  finish  bottles.  Seal. 
Pasteurize  in  water  at  180-185°  F.  for  30  minutes. 

To  use  for  making  jelly,  add  an  equal  volume  of  sugar  and  boil  to 
the  jellying  point. 

It  will  be  noted  that  10°  Balling  is  recommended,  although  experi- 
ments proved  that  a  juice  of  8°  Balling  would  give  a  good  jelly. 
Plums  vary  considerably  in  pectin  and  acid  and  it  is  desirable,  there- 
fore, to  add  a  safety  factor  of  2a  Balling. 

Candy  amd  Candy  Base. — Plums  are  rich  in  pectin  and  acid,  and, 
on  this  account,  plum  pulp  when  cooked  with  the  proper  proportion 
of  sugar  gives  a  very  firm  jelly-like  product  suitable  for  coating  with 
chocolate  or  sugar  as  a  confection. 

Plum  pulp  was  prepared  as  previously  described  for  jam  and  was 
then  concentrated  to  approximately  one-half  its  original  volume  in 
order  to  increase  the  pectin  content.  One  part  by  weight  of  this 
candy  base  with  one  part  of  sugar  cooked  to  222°-223°  F.  gave  on 
cooling,  a  very  firm  product  which  could  be  cut  into  suitable  form 
for  use  as  candy.  For  dipping  in  chocolate  it  was  found  desirable 
to  pour  the  hot  liquid  into  starch  molds  as  candy  manufacturers  do 
with  other  "jelly  center"  candies,  and  to  dry  the  centers  a  short  time 
at  120-130°  F.  so  that  the  surface  would  be  dry  enough  to  take  the 
chocolate  coating  satisfactorily.  Moisture  causes  the  chocolate  to 
turn  gray. 

In  addition  to  using  the  concentrated  pulp  in  preparing  candy,  it 
was  canned  boiling  hot  without  the  addition  of  sugar.    The  cans  were 


Bull.  400]  THE  utilization  of  surplus  plums  15 

sealed  and  sterilized  at  212°  F.  for  15  minutes.  The  canned  pulp 
has  kept  satisfactorily  for  two  years  and  its  jellying  power  has  not 
noticeably  decreased  during  storage. 

A  candy  base  was  also  prepared  with  equal  volume  of  unconcen- 
trated  Elberta  peach  pulp  and  plum  pulp  (from  mixed  varieties), 
plus  1  per  cent  by  weight  of  powdered  apple  pectin  containing  80 
per  cent  of  pectin.  The  pectin  was  dissolved  in  water  before  addition 
to  the  pulp.  This  product  also  gave  satisfactory  jelly  centers  when 
concentrated  to  222-223°  F.  with  an  equal  weight  of  sugar.  The 
unsweetened  pulp  was  canned  in  the  same  manner  as  the  plum  candy 
base  and  has  retained  its  jellying  power  and  flavor  satisfactorily  for 
two  years. 

The  inner  surface  of  the  cans  shows  considerable  etching  after  two 
years'  storage,  and  one  per  cent  of  the  cans  have  become  hydrogen 
swells.  After  one  year's  storage,  there  was  very  little  evidence  of 
action  on  the  tin  plate  and  there  were  no  hydrogen  swells. 

At  the  present  time,  most  candy  makers  use  starch,  agar  agar 
and  gelatin  in  preparing  jelly  centers.  Some  make  use  of  fruit  pulp 
with  or  without  the  addition  of  jellying  substances.  A  large  propor- 
tion of  glucose  is  used  in  such  candies  and  is  desirable  because  it 
prevents  crystallizing.  Several  manufacturers  stated  that  they  have 
used  plum  pulp  for  jelly  centers  and  found  it  satisfactory.  Its  use 
for  candy  centers  is,  therefore,  not  entirely  new  and  possibly  it  could 
be  introduced  to  the  commercial  manufacturers  as  well  as  to  house- 
wives. 

The  candy  base  is  excellent  for  jam  if  IV2  to  2  parts  of  sugar  is 
added  to  1  part  by  weight  of  the  pulp  and  the  mixture  cooked  to  the 
desired  consistency.  Because  of  its  double  utility  it  should  appeal 
particularly  to  housewives. 

Its  cost  is  moderate.  The  yield  of  plum  pulp  concentrated  2  :1  is 
about  100  gallons,  or  about  400  number  2%  cans  per  ton  of  fresh 
fruit.  With  fruit  at  $15  per  ton,  400  cans  at  $14.00,  labor  estimated 
at  $6.00  and  other  costs  at  2c  per  can  or  $8.00  per  ton,  the  cost  for 
400  cans  of  pulp  would  be  $43.00,  or  about  lie  a  can.  One  number 
2%  can  yields  about  3  pounds  of  candy.  At  a  retail  cost  of  20c  per 
can  for  the  pulp  and  15  cents  for  the  sugar  used,  the  cost  of  materials 
for  1  pound  of  candy  would  be  about  12  cents. 

The  plum  candy  is  pleasing  in  flavor  and,  because  of  its  acidity 
and  large  proportion  of  fruit,  should  be  more  wholesome  than  plain 
sugar  candies.  Because  of  its  cheapness,  ease  of  utilization,  pleasing 
flavor  and  health  appeal,  the  canned  candy  base  should  find  favor,  if 
not  for  commercial  use,  at  least  for  home  use. 


16  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Possibly  for  confectioner's  use  the  pulp  should  be  concentrated 
with  glucose  and  cane  suger  to  the  jellying  point,  poured  into  forms 
and  allowed  to  solidify  to  slabs,  dusted  with  powdered  sugar  or  starch 
and  packed  in  boxes  between  parraffin  paper.  The  confectioner  would 
then  have  only  to  cut  the  slabs  into  pieces,  roll  them  in  sugar  and 
pack  in  boxes  for  sale.    This  was  done  experimentally. 

Syrup  for  Beverage  and  Table  Use. — From  several  varieties  of 
plums  which  yielded  red  juices,  syrups  suitable  for  fountain  and  for 
domestic  use  were  prepared.  Syrup  made  from  white  varieties  was 
not  very  attractive  in  appearance. 

Because  of  its  very  high  acidity  and  deep  color,  the  Blue  Diamond 
variety  was  used  in  a  semi-commercial  scale  experiment,  although  in 
a  small  scale  test  the  Satsuma  was  found  to  give  a  syrup  of  more  pro- 
nounced flavor. 

Approximately  300  pounds  of  the  plums  were  placed  in  a  jelly 
kettle  with  water  to  cover  (about  10  gallons)  and  heated  to  180°  F. 
for  30  minutes.  This  softened  the  fruit  thoroughly  and  caused  the 
water  to  dissolve  the  color  from  the  skins.  The  hot  mixture  was 
placed  in  sugar  bags  of  double  thickness  and  allowed  to  drain  about 
15  hours.  The  juice  so  obtained  was  filtered  through  a  jelly  bag.  The 
yield  was  at  the  rate  of  about  160  gallons  per  ton  of  fresh  fruit.  It 
would  have  been  considerably  greater  if  pressure  could  have  been 
applied. 

The  juice  was  of  8°  Balling  and  contained  1.25  per  cent  acid  (as 
citric)  ;  juice  expressed  from  crushed  whole  plums  of  another  variety 
(Grand  Duke)  not  admixed  with  water  was  of  17°  Balling  and  1.45 
per  cent  acid. 

To  this  juice  sugar  was  added  to  increase  the  Balling  degree  from 
the  original  8°  to  35°  Balling.  It  was  sealed  cold  in  12  ounce  crown 
finish  bottles  and  hot  in  number  10  cans  and  pasteurized  at  180°  F. 
for  40  minutes.  The  juice  in  the  bottles  retained  its  color  satisfactory 
for  more  than  a  year,  but  that  in  the  tin  rapidly  changed  to  a  muddy, 
light  blue  color.  Bottled  unsweetened  juice  did  not  retain  its  flavor 
and  became  rather  astringent.  The  addition  of  sugar  appears  to  be 
necessary. 

The  sweetened  juice  made  an  excellent  beverage  when  diluted  with 
3  volumes  of  water  and  served  ice  cold.  It  was  served  in  this  form 
at  the  hotel  soda  fountain  in  Lincoln  and  proved  popular.  It  was 
much  improved  by  the  addition  of  10  to  20  per  cent  of  fresh  orange 
juice.  Because  of  its  high  acidity  and  deep  color,  it  was  found  to 
be  a  good  base  for  fruit  punches. 


BULL.  400]  TIIE  UTILIZATION   OF  SURPLUS   PLUMS  17 

In  preparing  the  fountain  syrup  on  a  commercial  scale,  it  is 
recommended  that  a  glass  lined  or  aluminum  kettle  instead  of  copper  be 
used  for  heating  the  fruit  in  order  to  avoid  loss  of  color,  and  that  the 
juice  be  recovered  from  the  heated  fruit  by  pressing  in  a  rack  and 
cloth  press  instead  of  by  draining  through  bags.  See  figure  4. 
Filtration  through  cotton  filter  pulp  in  a  Kieffer,  Cellulo  or  similar 
filter  would  give  a  clearer  juice  than  was  obtained  by  nitration 
through  a  felt  bag. 

It  is  believed  that  the  following  estimates  of  the  cost  of  materials 
and  manufacture  are  conservative. 

Estimated  cost  of 
Item  syrup  per  quart 

bottle 

Fruit  at  $20.00  per  ton  and  yield  at  175  gallons  per  ton 2.9c 

Sugar,  0.6  lb.  at  7c  per  pound 4.2c 

Bottle  at  5c 5.0c 

Manufacturing   cost    (labor,  power,   etc.) 2.5c 

Case,  label,  wrapping,  etc 4.0c 

Total  18.6c 

Because  of  its  succesful  trial  sale  as  a  fountain  beverage  at  Lincoln, 
it  is  believed  that  a  considerable  quantity  of  sweetened  juice  could 
be  sold  in  the  Sacramento  and  San  Joaquin  valleys  for  use  in  preparing 
summer  beverages,  for  fountain  and  home  use. 

In  addition  to  its  suitability  for  beverage  purposes,  the  syrup 
would  be  excellent  for  use  in  gelatin  desserts,  fruit  cocktails,  pudding 
sauces  (when  thickened  with  starch)  and  for  making  jelly  when 
pectin  (such  as  Certo)  and  sugar  are  added. 

Canning. — Some  of  the  plums,  particularly  those  too  small  for 
fresh  packing,  but  free  from  blemishes,  and  those  too  ripe  for  fresh 
shipment,  are  satisfactory  for  canning  purposes.  Several  varities 
were  canned,  of  these  the  Giant,  on  account  of  its  large  size  and 
relatively  low  acidity,  was  the  most  satisfactory.  The  President,  the 
Grand  Duke,  Santa  Rosa,  Wickson  and  Kelsey  plums  and  the  Sugar 
prune  gave  good  dessert  fruits  when  canned. 

In  some  experiments  sweet  varieties,  such  as  the  Giant  plum  and 
sugar  prunes  were  canned  in  plain  syrup  of  40°  Balling  and  the 
sourer  varieties,  such  as  the  Grand  Duke,  Santa  Rosa  and 
President  in  50°  Balling.  The  fruit  softens  during  steriliz- 
ing, and,  on  this  account,  the  sterilizing  period  should  be  short — not 
more  than  10  minutes  at  212°  F. — and  cooling  after  sterilizing  should 
be  thorough.    An  exhaust  of  6  minutes  at  200-210°  F.  was  used. 

In  some  experiments,  spiced  syrup  was  added  to  the  fruit  at  the 
time  of  canning.     The  spiced  plums  were  preferred  to  the  unspiced 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

by  those  who  sampled  them.  Because  of  their  natural  high  acidity, 
it  is  not  necessary  to  add  vinegar  to  the  spiced  syrup  as  is  done  with 
peaches  and  pears.     The  recommended  procedure  is  as  follows : 

Sort,  wash  and  can  the  fruit.  Add  a  syrup  of  40°  Balling 
previously  spiced  by  heating  to  boiling  20  gallons  of  syrup  with  12 
ounces  of  ginger  root,  14  ounces  of  whole  cloves,  18  ounces  stick 
cinnamon  and  14  ounces  whole  allspice,  allowing  to  stand  8-12  hours 
and  straining  through  cheese  cloth  to  remove  the  spices.  Exhaust 
6  minutes.  Seal.  Process  8-10  minutes  at  212°  F.  and  cool 
thoroughly. 

Preserves. — The  sour  varieties  of  plums  gave  fairly  satisfactory 
preserves  when  boiled  a  short  time,  4-5  minutes,  with  an  equal  weight 
of  sugar  and  barely  enough  water  to  prevent  scorching.  The  fruit 
was  allowed  to  stand  overnight  in  the  syrup  formed  during  cooking 
in  order  to  permit  absorption  of  the  syrup  by  the  fruit.  The  preserves 
were  packed  in  4  ounce  and  8  ounce  vacuum  sealed  jars  and  sterilized 
at  185°  F.  for  40  minutes. 

It  was  found  by  A.  W.  Christie  that  most  varieties  could  be  peeled 
in  the  same  manner  as  tomatoes — -that  is,  by  hand  after  heating  in 
boiling  water  about  3  minutes  and  chilling  in  cold  water.  The  peeled 
fruit  was  used  experimentally  in  making  preserves  as  described  above 
and  for  packing  in  glass  in  a  spiced  syrup.  This  syrup  was  made  with 
16  pounds  of  sugar,  3  pints  of  40  grain  vinegar  and  7  pints  of  water. 
To  this  quantity  of  syrup  were  added  1  ounce  of  ginger  root,  2  ounces 
whole  cloves  and  3  ounces  of  stick  cinnamon.  The  syrup  and  spices 
were  brought  to  boiling  for  2  or  3  minutes  and  allowed  to  stand  over- 
night. The  plums,  both  peeled  and  unpeeled,  were  heated  to  boiling 
in  this  syrup  and  allowed  to  stand  overnight.  They  were  then  packed 
in  vacuum  sealed  jars  and  sterilized  at  185°  F.  for  30  minutes. 

Plum  preserves  and  jams  are  not  in  such  great  demand  as  those 
made  from  berries;  nevertheless,  the  plum  products  are  good  for 
table  use  and  can  be  made  more  cheaply  than  the  berry  products  on 
account  of  the  low  cost  of  the  cull  plums.  If  sold  at  a  low  price,  a 
considerable  quantity  of  plums  might  be  disposed  of  in  the  form  of 
preserves  and  jam. 

Dehydration*. — Nine  varieties  of  plums  from  Placer  County  were 
dehydrated  experimentally  and  the  cooking  quality  of  the  dehydrated 
products  determined.  The  Santa  Rosa,  Blue  Diamond,  Wickson  and 
Climax  gave  satisfactory  dried  products,  with  the  Santa  Rosa  ranking 


*  The  experiments  on  dehydration  were  made  by  Professor  A.  W.  Christie,  to 
whom  thanks  are  due  for  data  on  dehydration  used  in  this  publication. 


Bull.  400]  THe  utilization  of  surplus  plums  19 

first  in  quality.  The  Burbank,  Kelsey,  Grand  Duke  and  Giant  gave 
only  fair  results,  while  the  California  Blue  was  very  poor  in  quality 
after  drying. 

The  fruit  used  in  these  experiments  was  picked  green  for  Eastern 
shipment  and  allowed  to  ripen  in  the  crates.  If  allowed  to  ripen  on 
the  trees,  it  would  have  become  richer  in  sugar  and,  therefore  of 
better  drying  quality. 

The  immaturity  of  the  fruit  was  reflected  also  in  the  yields;  the 
drying  ratios  (ratio  of  fresh  to  dried  weights)  were  high,  varying 
from  4.3  :1  to  6.8  :1,  averaging  5.3  :1.  French  prunes  average  about 
2.3:1. 

In  preparing  the  plums  for  drying,  it  was  found  desirable  to  dip 
them  in  a  boiling  dilute  lye  solution  (about  %-%  of  1  per  cent)  to 
check  the  skins.  Exposure  of  the  lye  dipped  fruit  to  the  fumes  of 
burning  sulphur  for  30-60  minutes  retained  the  natural  color  of  the 
fruit  and  checked  darkening. 

A  drying  temperature  of  150°  F.  was  found  best.  Higher  tempera- 
tures caused  "bleeding"  of  the  fresh  fruit  and  darkening  near  the 
end  of  the  drying  period.  In  order  to  have  the  fruit  keep  well,  the 
moisture  content  of  the  dried  product  must  be  low  because  the  low 
sugar  content  of  the  fruit  renders  it  susceptible  to  molding. 

The  cost  of  dehydrating  would  probably  be  about  the  same  per 
green  ton  as  for  prunes,  although  greater  per  dry  pound,  because  of 
the  higher  drying  ratio  of  the  plums,  A.  W.  Christie  estimates  the 
direct  dehydrating  cost  at  about  1  cent  per  pound  and  costs  of 
maintaining  a  plant,  processing,  packing,  selling,  etc.,  at  4-5  cents 
per  dry  pound  additional.  On  this  basis,  the  dried  plums  would  have 
to  sell  wholesale  at  10  cents  a  pound  to  return  the  grower  $15.00- 
$20.00  per  green  ton. 

Dehydrated  plums  would  probably  have  to  compete  with  dried 
prunes  and,  since  the  plums  require  the  addition  of  sugar  and  prunes 
do  not,  they  would  be  at  a  considerable  disadvantage.  However,  the 
dehydrated  plums  are  excellent  as  a  raw  material  for  the  making  of 
jam,  jelly  and  preserves  and  for  use  in  pies — for  which  the  sweet 
varieties  of  dried  prunes  are  not  well  adapted.  Like  all  new  products, 
dehydrated  plums  would  require  advertising  to  introduce  them 
successfully. 


20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


SUMMARY  AND  CONCLUSIONS 

1.  List  of  Products. — During  the  1923,  1924,  and  1925  seasons 
various  products  were  prepared  from  cull  shipping-  plums.  A  list 
of  these  products  and  estimated  cost  of  each  is  given  in  the  accom- 
panying table. 


Product 

Container  recommended 

Estimated  cost  of  production 

Frozen  crushed  plums 

for  jam  and  jelly. 
Butter  and  jam 

5  gallon  tins  and  50  gallon 

barrels. 
No.  1  tall  and  No.  10  cans; 

8  oz.  and  16  oz.  jars. 

No.  2l/2,  No.  10  and  5  gallon 

cans. 
No.  2Y2,  No.  10  and  5  gallon 

cans. 
8  oz.  and  16  oz.  jars;  No.  10 

cans. 
12  oz.  bottles;  quart  bottles 

and  5  gallon  lacquered  cans 
1  pound  boxes 

23^c  per  pound  or  22c  per 

gallon. 
No.  1  tall  can  7.5c;  No.   10 

Plum  jam  pulp 

cans  69c;  8  oz.  jar  6c;  16 
oz.  jar  lie. 

No.  2}/2  can  81^c;  No.  10  can 

Plum-peach  jam  pulp  . 
Jelly 

27>2c;  5  gallon  can  $1.50. 
No.  2l/2  can  8%c;  No.  10  can 

29c;  5  gallon  can  $1.55. 
8  oz.  jar  7c;  16  oz.  jar  lie; 

No.  10  can  80c. 
12  oz.  bottle  5c;  quart  bottle 

13c;  5  gallon  can  $1.70. 
15c  per  pound. 
No.  2x/2  can  lie;  No.  10  can 

Jelly  juice 

Candy 

Candy  base 

No.  2x/2  and  No.  10  cans 

Quart  and  gallon  bottles 

8  oz.  and  16  oz.  jars 

Beverage  syrup 

35c. 
Quart  18.6c;  gallon  68c. 
8  oz.  jars  7c;  16  oz.  jar  lie. 
No.  2l/2  can  8-10c. 

Preserves 

Canned  plums 

No.  2]4  cans 

Dehydrated  plums 

1  pound  and  5  pound  cartons.. 

1     pound    carton    9-10c;    5 
pound  carton  43-47c. 

2.  Freezing  Storage. — Cull  plums  may  be  crushed  in  an  ordinary 
apple  crusher  and  packed  in  barrels  or  5  gallon  cans  and  stored 
indefinitely  at  a  freezing  temperature  for  use  in  jams  and  jellies. 
After  removal  from  storage  the  fruit  will  keep  at  least  one  week  in 
50  gallon  barrels.  This  makes  possible  its  transportation  to  consid- 
erable distances  without  additional  refrigeration.  This  method  is 
recommended  above  all  others  for  preserving  plums  for  use  in  jam 
factories  on  the  Pacific  Coast. 

3.  Butter  and  Jam. — Cull  plums  of  sound  quality  are  as  good  as 
higher  priced  first  quality  plums  for  use  in  jam  and  butter  and  should 
find  a  considerable  market  for  use  in  low  priced  jams  and  butters. 
Cull  shipping  peaches  may  be  used  with  the  plums  to  advantage. 

4.  Jam  Pidp. — A  low  priced  jam  pulp  suitable  for  home  and 
factory  use  may  be  prepared  from  cull  plums  by  heating  until  soft 


Bull.  400]  TIIE  utilization  of  surplus  plums  21 

and  pulping  through  a  coarse  tomato  pulper  screen  or,  preferably,  a 
special  very  coarse  screen  in  a  tomato  pulp  finisher.  This  product 
could  probably  be  retailed  for  15  cents  per  No.  2%  (quart)  can. 
Peach  pulp  from  cull  shipping  peaches  added  to  the  plum  pulp 
improves  the  flavor. 

5.  Jetty. — Cull  plums  are  perfectly  satisfactory  for  jelly  making. 
Varieties  yielding  red  juice  high  in  acidity  such  as  Blue  Diamond, 
Santa  Rosa,  Satsuma  and  California  Blue  are  recommended  in  pref- 
erence to  white  varieties. 

6.  Jelly  Juice. — A  low  priced,  but  excellent  juice  for  jelly  may 
be  prepared  from  cull  plums  by  cooking  the  fruit,  extracting  the 
juice  as  for  jelly  making  and  pasteurizing  it  in  bottles  for  home  and 
factory  use.     Sugar  is  added  by  the  user. 

7.  Candy  and  Candy  Base. — Plum  pulp  concentrated  2:1  makes 
an  excellent  candy  center  when  cooked  to  222°  F.  with  an  equal 
weight  of  sugar.  The  pulp  may  be  canned  without  sugar  for  use 
by  confectioners  and  housewives.  Jam  pulp  may  be  used  for  the  same 
purpose. 

8.  Beverage  Syrup. — Red  plum  juice  sweetened  with  cane  sugar 
to  35°  Balling  is  an  excellent  base  for  summer  beverages.  It  should 
find  a  ready  market  in  the  hot  interior  valleys  of  the  State. 

9.  Preserves. — Both  plain  and  spiced  preserves  of  good  quality 
can  be  made  from  unblemished  cull  plums  by  standard  formulae. 

10.  Canning. — -Several  varieties  of  unblemished  cull  shipping 
plums  were  found  thoroughly  satisfactory  for  canning  for  dessert 
purposes.  A  spiced  syrup  is  recommended.  The  larger  varieties  are 
probably  to  be  preferred  for  canning. 

11.  Dehydrated  Plums. — Most  varieties  of  cull  plums  give  fairly 
satisfactory  dehydrated  products,  but  the  yield  is  low.  The  dried 
fruit  is  very  tart  and  requires  the  addition  of  sugar  when  cooked 
for  sauce  or  jam. 

Recommendations 

It  is  recommended  that  plum  growers  and  shippers  arrange  with 
existing  fruit  products  establishments  for  the  trial  production  of 
several  of  the  most  promising  products  described  in  this  bulletin  and 
that  their  marketability  and  profitability  be  determined  by  trial 
sales. 

For  such  trials  frozen  plums  in  barrels,  plum  butter,  plum  jam 
pulp,  plum  jelly  juice  and  plum  beverage  syrup  are  recommended. 
These  products  are  listed  in  the  order  of  their  supposed  desirability 
and  chance  of  commercial  success. 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 


BULLETINS 


No.  No. 

253.   Irrigation   and   Soil   Conditions   in  the  363. 

Sierra   Nevada   Foothills,    California. 

261.  Melaxuma    of    the    Walnut,     "Juglans  364. 

regia." 

262.  Citrus   Diseases   of   Florida    and   Cuba  365. 

Compared  with  Those  of  California.  366 

263.  Size   Grades   for  Ripe   Olives. 

268.   Growing  and  Grafting  Olive  Seedlings.  367. 

273.   Preliminary  Report  on  Kearney  Vine- 
yard  Experimental   Drain.  368. 

275.  The     Cultivation     of     Belladonna     in 

California.  369. 

276.  The  Pomegranate. 

277.  Sudan    Grass.  370. 

278.  Grain    Sorghums.  3  71. 

279.  Irrigation   of   Rice   in   California. 

280.  Irrigation    of    Alfalfa    in    the    Sacra-  372. 

mento  Valley. 
283.   The   Olive   Insects  of  California.  373. 

285.  The  Milk   Goat   in   California.  374. 

294.   Bean   Culture  in   California. 
304.  A   Study  of  the  Effects  of  Freezes  on 

Citrus    in    California.  375. 

310.   Plum    Pollination. 

312.  Mariout   Barley.  376. 

313.  Pruning      Young      Deciduous      Fruit 

Trees.  377. 

319.   Caprifigs    and    Caprification.  379. 

324.  Storage  of   Perishable  Fruit  at  Free'z-  380. 

ing  Temperatures. 

325.  Rice     Irrigation     Measurements      and  381. 

Experiments    in    Sacramento    Valley, 
1914-1919.  382. 

328.   Prune    Growing   in    California. 

331.   Phylloxera-Resistant    Stocks.  383. 

334.  Preliminary    Volume    Tables    for    Sec- 

ond-Growth  Redwood.  384. 

335.  Cocoanut    Meal    as    a    Feed   for   Dairy 

Cows    and    Other   Livestock. 

339.  The    Relative    Cost    of    Making    Logs 

from   Small   and  Large  Timber.  385. 

340.  Control     of     the     Pocket     Gopher     in  386. 

California. 

343.  Cheese    Pests    and    Their    Control.  387. 

344.  Cold    Storage    as    an   Aid   to    the   Mar-  388. 

keting  of  Plums. 

346.  Almond    Pollination.  389. 

347.  The  Control  of  Red  Spiders  in  Decid-  390. 

uous  Orchards. 

348.  Pruning  Young  Olive  Trees.  391. 

349.  A     Study    of    Sidedraft    and    Tractor 

Hitches.  392. 

350.  Agriculture      in      Cut-over      Redwood  394. 

Lands. 

352.  Further  Experiments  in  Plum  Pollina-  395. 

tion.  396. 

353.  Bovine   Infectious   Abortion. 

354.  Results  of  Rice  Experiments  in   1922.  397. 

357.  A     Self-mixing    Dusting    Machine    for 

Applying      Dry       Insecticides       and  398. 

Fungicides.  399. 

358.  Black    Measles,     Water    Berries,     and 

Related  Vine  Troubles. 

359.  Fruit   Beverage   Investigations.  400. 

361.  Preliminary    Yield    Tables    for    Second 

Growth   Redwood. 

362.  Dust  and  the  Tractor   Engine. 


The  Pruning  of  Citrus  Trees  in  Cali- 
fornia. 

Fungicidal  Dusts  for  the  Control  of 
Bunt. 

Avocado  Culture  in  California. 

Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Methods  of  Harvesting  and  Irrigation 
in   Relation   of  Mouldy  Walnuts. 

Bacterial  Decomposition  of  Olives  dur- 
ing Pickling. 

Comparison  of  Woods  for  Butter 
Boxes. 

Browning  of  Yellow  Newtown  Apples. 

The  Relative  Cost  of  Yarding  Small 
and   Large   Timber. 

The  Cost  of  Producing  Market  Milk  and 
Butterfat  on  246  California  Dairies. 

Pear    Pollination. 

A  Survey  of  Orchard  Practices  in  the 
Citrus  Industry  of  Southern  Cali- 
fornia. 

Results    of    Rice    Experiments    at    Cor- 

■    tena,    1923. 

Sun-Drying  and  Dehydration  of  Wal- 
nuts. 

The   Cold    Storage   of   Pears. 

Walnut   Culture    in   California. 

Growth  of  Eucalyptus  in  California 
Plantations. 

Growing  and  Handling  Asparagus 
Crowns. 

Pumping  for  Drainage  in  the  San 
Joaquin    Valley,    California. 

Monilia  Blossom  Blight  (Brown  Rot) 
of  Apricot. 

A  Study  of  the  Relative  Values  of  Cer- 
tain Succulent  Feeds  and  Alfalfa 
Meal  as  Sources  of  Vitamin  A  for 
Poultry. 

Pollination    of    the    Sweet    Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig   Smut. 

The  Principles  and  Practice  of  Sun- 
drying  Fruit. 

Berseem  or   Egyptian    Clover. 

Harvesting  and  Packing  Grapes  in 
California. 

Machines  for  Coating  Seed  Wheat  with 
Copper    Carbonate    Dust. 

Fruit    Juice    Concentrates. 

Cereal  Hay  Production  in  California. 
Feeding  Trials  with  Cereal  Hay. 

Bark   Diseases   of   Citrus  Trees. 

The  Mat  Bean  (Phaseolus  aconilifo- 
lius). 

Manufacture  of  Roquefort  Type  Cheese 
from   Goat's   Milk. 

Orchard  Heating  in  California. 

The  Blackberry  Mite,  the  Cause  of 
Redberry  Disease  of  the  Himalaya 
Blackberry,    and    its    Control. 

The  Utilization  of  Surplus  Plums. 


No. 

87 

113 

117 


Alfalfa. 

Correspondence  Courses  in  Agriculture. 
The    Selection    and    Cost    of    a    Small 
Pumping  Plant. 
127.   House    Fumigation. 
129.  The   Control  of   Citrus   Insects. 
136.   Melilotus    indica    as    a    Green-Manure 
Crop  for  California. 


CIRCULARS 
No. 
144 


Oidium    or    Powdery    Mildew    of    the 
Vine. 

Feeding  and   Management  of   Hogs. 

Some  Observations  on  the  Bulk  Hand- 
ling of    Grain    in    California. 

Irrigation   Practice   in   Growing   Small 
Fruit   in    California. 
155.   Bovine  Tuberculosis. 


151 
152 


154. 


CIRCULARS—  C  Continued ) 


No. 

15  7. 

160. 

164. 

166. 

167. 

170. 

173. 

178. 
179. 

184. 
190. 
199. 

202. 

203. 
209. 
210. 
212. 
214. 

215. 

217. 

220. 

228. 
230. 

231. 
232. 

233. 
234. 

235. 

236. 


237. 

238. 
239. 

240. 

241. 

242. 
243'. 

244 
245. 
247. 
248. 

249. 

250. 

251. 


252. 
253. 
254. 

255. 


Control  of  the  Pear   Scab. 

Lettuce   Growing  in   California. 

Small  Fruit  Culture  in  California. 

The   County  Farm  Bureau. 

Feeding    Stuffs    of   Minor    Importance. 

Fertilizing  California  Soils  for  the 
1918   Crop. 

The  Construction  of  the  Wood-Hoop 
Silo. 

The   Packing  of  Apples   in   California. 

Factors  of  Importance  in  Producing 
Milk  of  Low  Bacterial   Count. 

A   Flock   of    Sheep   on   the   Farm. 

Agriculture  Clubs  in   California. 

Onion    Growing   in    California. 

County  Organizations  for  Rural  Fire 
Control. 

Peat   as    a   Manure    Substitute. 

The  Function  of  the  Farm  Bureau. 

Suggestions  to  the  Settler  in  California. 

Salvaging    Rain-Damaged    Prunes. 

Seed  Treatment  for  the  Prevention  of 
Cereal   Smuts. 

Feeding  Dairy  Cows  in  California. 

Methods  for  Marketing  Vegetables  in 
California. 

Unfermented   Fruit   Juices. 

Vineyard   Irrigation  in  Arid  Climates. 

Testing  Milk,  Cream,  and  Skim  Milk 
for  Butterfat. 

The    Home    Vineyard. 

Harvesting  and  Handling  California 
Cherries    for    Eastern    Shipment. 

Artificial    Incubation. 

Winter  Injury  to  Young  Walnut  Trees 
during   1921-22. 

Soil  Analysis  and  Soil  and  Plant 
Inter-relations. 

The  Common  Hawks  and  Owls  of 
California  from  the  Standpoint  of 
the  Rancher. 

Directions  for  the  Tanning  and  Dress- 
ing of  Furs. 

The  Apricot  in  California. 

Harvesting  and  Handling  Apricots 
and  Plums  for  Eastern   Shipment. 

Harvesting  and  Handling  Pears  for 
Eastern   Shipment. 

Harvesting  and  Handling  Peaches  for 
Eastern    Shipment. 

Poultry  Feeding. 

Marmalade  Juice  and  Jelly  Juice  from 
Citrus  Fruits. 

Central  Wire  Bracing  for  Fruit  Trees. 

Vine   Pruning   Systems. 

Colonization    and    Rural   Development. 

Some  Common  Errors  in  Vine  Prun- 
ing and  Their  Remedies. 

Replacing    Missing t  Vines. 

Measurement  of  Irrigation  Water  on 
the  Farm. 

Recommendations  Concerning  the  Com- 
mon Diseases  and  Parasites  of 
Poultry   in   California. 

Supports  for  Vines. 

Vineyard  Plans. 

The  Use  of  Artificial  Light  to  Increase 
Winter    Egg    Production. 

Leguminous  Plants  as  Organic  Fertil- 
izer   in    California    Agriculture. 


No. 

256. 

257. 

258. 

259. 

260. 

261. 
262. 
263. 
264. 

265. 
266. 

267. 

268. 

269. 

270. 
271. 
272. 

273. 
274. 

275. 

276. 
277. 


279. 

281. 

282. 

283. 
284. 
285. 
286. 
287. 
288. 
289. 
290. 
291. 

292. 
293. 
294. 
295. 

296. 

297. 

298. 

299. 
300. 
301. 
302. 
303. 


The    Control   of  Wild   Morning   Glory. 

The  Small-Seeded  Horse  Bean. 

Thinning   Deciduous    Fruits. 

Pear  By-products. 

A  Selected  List  of  References  Relating 
to  Irrigation  in  California. 

Sewing  Grain  Sacks. 

Cabbage   Growing  in  California. 

Tomato  Production  in  California. 

Preliminary  Essentials  to  Bovine 
Tuberculosis  Control. 

Plant   Disease   and   Pest   Control. 

Analyzing  the  Citrus  Orchard  by 
Means   of    Simple   Tree   Records. 

The  Tendency  of  Tractors  to  Rise  in 
Front;    Causes   and   Remedies. 

Inexpensive  Labor-saving  Poultry  Ap- 
pliances. 

An  Orchard  Brush  Burner. 

A  Farm  Septic  Tank. 

Brooding    Chicks    Artificially. 

California  Farm  Tenancy  and  Methods 
of  Leasing. 

Saving  the   Gophered   Citrus  Tree. 

Fusarium  Wilt  of  Tomato  and  its  Con- 
trol by  Means  of  Resistant  Varieties. 

Marketable  California  Decorative 
Greens. 

Home  Canning. 

Head,  Cane,  and  Cordon  Pruning  of 
Vines. 

Olive  Pickling  in  Mediterranean  Coun- 
tries. 

The  Preparation  and  Refining  of  Olive 
Oil   in    Southern    Europe. 

The  Results  of  a  Survey  to  Determine 
the  Cost  of  Producing  Beef  in  Cali- 
fornia. 

Prevention  of  Insect  Attack  on  Stored 
Grain. 

Fertilizing  Citrus  Trees  in  California. 

The  Almond   in    California. 

Sweet  Potato  Production  in  California. 

Milk  Houses  for  California  Dairies. 

Potato    Production   in    California. 

Phylloxera   Resistant  Vineyards. 

Oak  Fungus  in  Orchard  Trees. 

The  Tangier  Pea. 

Blackhead  and  Other  Causes  of  Loss 
of  Turkeys  in   California. 

Alkali   Soils. 

The    Basis    of    Grape    Standardization. 

Propagation   of   Deciduous   Fruits. 

The  Growing  and  Handling  of  Head 
Lettuce   in    California. 

Control  of  the  California  Ground 
Squirrel. 

A  Survey  of  Beekeeping  in  California ; 
The  Honeybee  as  a  Pollinizer. 

The  Possibilities  and  Limitations  of 
Cooperative  Marketing. 

Poultry    Breeding   Records. 

Coccidiosis  of  Chickens. 

Buckeye   Poisoning  of  the  Honey  Bee. 

The   Sugar   Beet   in   California. 

A  Promising  Remedy  for  Black  Measles 
of   the   Vine. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 

lOm-2,'26 


